The Min system is not required for precise placement of the midcell Z ring in Bacillus subtilis.

1School of Molecular and Microbial Biosciences, University of Sydney, Sydney, NSW 2006, Australia.

Abstract

In bacteria, the Min system plays a role in positioning the midcell division site by inhibiting the formation of the earliest precursor of cell division, the Z ring, at the cell poles. However, whether the Min system also contributes to establishing the precise placement of the midcell Z ring is unresolved. We show that the Z ring is positioned at midcell with a high degree of precision in Bacillus subtilis, and this is completely maintained in the absence of the Min system. Min is therefore not required for correct midcell Z ring placement in B. subtilis. Our results strongly support the idea that the primary role of the Min system is to block Z ring formation at the cell poles and that a separate mechanism must exist to ensure cell division occurs precisely at midcell.

Z ring position in B. subtilis cells grown out from spores or vegetatively growing cells. Z ring position is given by the ratio of the shorter distance from a cell pole to the total cell length. (A) FtsZ distribution in outgrown spores of dna-1 (MinCD+) processed for IFM. (B) FtsZ distribution in the absence of MinCD in outgrown spores of SU429 processed for IFM. (C) FtsZ distribution in the absence of MinCD in vegetative cells of SU429 processed for IFM. (D) FtsZ–YFP distribution in live outgrown spores of strain SU434 (MinCD+). (E and F) FtsZ–YFP distribution in the absence of MinCD in live outgrown spores of SU433 and SU440, respectively. The additional numbers show the number of cells scored (upper) and the mean cell length in micrometres (lower).

Z rings visualized as an FtsZ–YFP fusion in live cells grown out from B. subtilis spores. (A) A midcell Z ring in SU434 (MinCD+). Midcell Z rings (B) and polar Z rings (C) detected in the MinCD− strain, SU433. The image on the right in (B) and (C) shows autofluorescence of the spore coats attached to the cell ends. The arrow on the right image in (C) shows the polar Z ring. Scale bar, 1 μm.